(a) Field of the Invention
This invention generally relates to a resilient plastic clip and method for making the clip. More particularly, but not by way of limitation, to a plastic clip having legs or arms that are preloaded or biased directly against one another when the clip is not in use.
(b) Discussion of Known Art
The advantaged of a clip made from spring materials have long been recognized for their simplicity and ease of use. Most known clips consist of a pair of legs or arms that are biased against one another by a spring. Many metal clips take advantage of the modulus of elasticity of sections of metal ribbon to produce an integral clip, having both legs and the spring biasing the legs towards one another made from a single, continuous, section of metal ribbon. Examples of this kind of device can be found in U.S. Pat. No. 609,486 to Wilson shows the use of metal ribbon to create a metal spring. The Wilson device also illustrates the use of legs of uneven length, the shorter leg having a sharp edge to allow the insertion of the short leg between spirals of coiled material, such as ribbon or paper.
Other examples of metal clips can be found in U.S. Pat. Nos. 1,675,286 to Van Valkenburg and 1,621,008 to Fricker. These devices take advantage of the elasticity of metal to provide a clip from a bent section of sheet-metal or metal ribbon. The advantages of sheet-metal or metal ribbon for the manufacture of clips have been difficult to overcome. An important factor that has made metal such an ideal choice for the making of spring clips is that sheet-metal is highly amenable to various cold-working processes that allow the clip to accept a bias, such that the legs of the clip are biased against one another.
While the mechanical properties of many metals lend themselves for the creation of highly effective clips, there remains a need for clips made from materials such as polymers, plastics that provide important mechanical properties that are not inherent in metals. For example, plastics are typically non-abrasive and non-conductive, and are thus innocuous to delicate surfaces or surfaces that must be insulated from electrical currents or protected from galvanic or stress corrosion. Unfortunately, however, it is difficult to take advantage of polymers, and particularly thermoplastics, in the making of spring loaded or biased devices such as clips due to the fact that the polymer must be molded into the shape of the clip. The molding of the material into the shape of the clip makes it difficult to arrive at a clip with legs that retain internal stresses that bias the legs against one another.
Additionally, there remains a need for a plastic, or polymer, clip that can be used for retaining large sections of material together without scarring or scraping the sections of material.
It has been discovered that the problems left unanswered by known art can be solved by providing a plastic clip of unitary, one piece construction, the clip including at least the following components:
a first leg that is of a first thickness, and a second leg that is of a second thickness, the first leg being biased against the second leg by an bridging section that is greater than the thickness of the first leg or the second leg.
According to a highly preferred embodiment of the invention, the legs of the clip may be of the same or different thickness. The bridging section, is of greater thickness to provide a stiff support for the legs.
The bias of the legs against one another is introduced into the disclosed clip by the molding process used to create the disclosed clip. This process uses a mold that has the legs spaced apart from one another. The mold accepts the thermoplastic material that will be used to form the disclosed clip, and allows the molten thermoplastic material to fill the cavity of the mold, defining the main components of the disclosed clip. Then, a portion of the bridging section is cooled at a faster rate than the remaining portions of the bridging section. This differential cooling introduces internal stresses into the bridging section to introduce a bias forcing the legs against one another.
In a preferred embodiment of the invention one of the legs includes a leading edge that is sloped or rounded towards the opposite leg. This sloping or rounded edge creates a leading edge that provides a smooth transition from a surface that is held between the two legs. It has been discovered that this smooth transition is particularly useful when using the disclosed clip for holding the flaps of containers, such as cardboard boxes, in an open position to allow loading and unloading of the containers. In this application, the tapered leading edge provides an unobtrusive transition between the internal surface of the box and the clip, prevent snagging and inadvertent removal of the clip when removing materials from the container.
Still further, it is contemplated that the leg opposite to the leg with the tapered leading edge will include a flared or bent end that will allow the user to capture materials between the two legs easily.
Thus, as illustrated by this summary, it should be understood that while the above and other advantages and results of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings, showing the contemplated novel construction, combinations and elements as herein described, and more particularly defined by the appended claims. It should also be clearly understood that changes in the precise embodiments of the herein disclosed invention are meant to be included within the scope of the claims, except insofar as they may be precluded by the prior art.